Solid oxide cells (SOC's) include cells designed for different applications, such as solid oxide fuel cells (SOFC's), or solid oxide electrolysis cells (SOEC's). These types of cells are well known in the art. Typically, a solid oxide fuel cell comprises an electrolyte layer sandwiched by two electrode layers. During operation, usually at a temperature from about 500° C. to about 1100° C., one electrode is in contact with oxygen or air and the other electrode is in contact with a fuel gas. In the case of SOFC's the cathode is in contact with oxygen or air and the anode is in contact with the fuel gas.
The most common manufacture processes suggested in the prior art comprise the manufacture of single cells, which are then stacked together for more power output. Generally, a support is provided, on which an anode layer is formed, followed by an electrolyte layer. The so formed half cell is then dried and sintered, occasionally under reducing atmosphere conditions. Finally, a cathode layer is formed on the sintered structure so as to obtain a complete cell.
The cells are usually manufactured by the use of wet powder processing techniques which comprise tape-casting of the support component. The cell support component is normally made by tape casting of a powder suspension and the active layers (cathode, electrolyte and anode) are subsequently deposited onto the support by spray painting or screen printing, with intermediate sintering steps for the different layers.
Alternatively, SOFC's are for instance manufactured by electrochemical vapour deposition (CVD) methods or plasma spraying. However, said processes are very expensive, and thus there has been a desire to lower the fabrication costs.
U.S. Pat. No. 5,803,934 relates to a method of producing an electrode layer on a solid electrolyte of a solid state fuel cell. Manually cast foils were made from a slurry and formed into a chromate tape. The chromate tapes were then laminated with a green 8 mol % Yttria stabilized zirconia tape by painting the corresponding surfaces of the tapes with ethanol and passing the laminates through a roller mill. The laminates were placed between fibrous alumina plates to prevent curling and sintered in air at 1,300° C. for 6 hours.
U.S. Pat. No. 5,846,664 relates to a process for the manufacture of a porous metal component. A colloidal suspension is provided, cast into a thin sheet and air dried to form a tape having pre-selected pliability properties. A predetermined number of tape layers is stacked and compacted between rollers, or layered in a die, or otherwise pre-formed and laminated. Lamination takes places at pressures ranging from between about 5 MPa to about 60 MPa at temperatures in the range of between about 25° C. to about 80° C. for a time effective to laminate said layers of tape and form a green body.
U.S. 2003/0231973 relates to a method for preparing compositionally graded metallic plates and compositionally graded metallic plates suitable for use as interconnects for solid oxide fuel cells. More specifically, plates with graded composition, from one side to the other, may be prepared by forming layers of different slips on top of each other or laminating together separately prepared green layers, using a small amount of solvent between the layers or warm pressing together. One process includes the lamination of separately prepared green layers optionally having a small amount of solvent painted between the layers to promote bonding. The green layers may also be compressed together. Functionally graded or laminated materials may be prepared by wiping a solvent on one or both surfaces of each layer and stacking multiple layers in the desired order. Theses multi-layers are then warm pressed to help ensure good adhesion between the layers.
U.S. Pat. No. 5,788,788 relates to a method of preparing a fuel cell element including the step of: laminating ceramic tapes to form an unfired anode/electrolyte laminate; reducing the thickness of the anode/electrolyte laminate; sintering the anode/electrolyte laminate; laminating ceramic tapes to form an unfired cathode/interconnect laminate; reducing the thickness of the cathode/interconnect laminate; embossing a gas flow path pattern into the cathode layer of the cathode/interconnect laminate; sintering the cathode/interconnect laminate; and bonding the sintered anode/electrolyte laminate to the sintered cathode/interconnect laminate such that the electrolyte layer contacts the cathode layer. The fabrication further typically involves reducing the thickness of the laminates, for example by rolling. The stack is passed between two rolls to laminate the two layers together in order to form an unfired anode/electrolyte laminate or cathode/interconnect laminate.
EP-A-1306920 relates to a unit cell for a fuel cell which is formed by laminating a fuel electrode, a solid electrolyte, and an air electrode on a porous base material. The fuel electrode of the unit cell can be made as a laminated body by laminating a plurality of fuel electrode layers. As may be seen from the examples, a Copper-made porous metal was obtained, a Samarium doped ceria layer was formed as a fuel electrode material, a Samarium doped ceria layer was formed as a solid electrolyte material, and the thus obtained sheets were layered on top of each other. The laminated sheets were afterwards pressurized at 100 g/cm2, whereby the adhesiveness among the various layers was enhanced.
WO-A2-03/036739 discloses solid oxide fuel cells made by coating a slurry of an electrolyte having a limited amount of organic material onto a carrier tape, depositing at least one layer electrode material on tape to support the electrolyte layer, removing the tape, screen printing a second electrode layer on the exposed surface of the electrolyte layer, and firing the layers at temperatures of 1100 to 1300° C.
U.S. Pat. No. 4,957,673 discloses a unitary layered ceramic structure which comprises co-sintered layers. The co-sintered structure comprises a sintered central layer of yttria stabilized zirconia, and sintered outer layers of strontium lanthanum manganite.
US-A-2006/0024547 relates to a fuel cell comprising a cathode, an electrolyte, an anode and a porous multifunctional layer disposed on the anode opposite to the electrolyte. The porous multifunctional layer comprises a cermet which has thermal expansion and shrinkage behaviour substantially similar to the other fuel cell layers.
WO-A-2006/082057 relates to a method of producing a reversible solid oxide fuel cell, comprising the steps of 1) providing a metallic support layer; 2) forming a cathode precursor layer on the metallic support layer; 3) forming an electrolyte layer on the cathode precursor layer; 4) sintering the obtained multilayer structure; 5) impregnating the cathode precursor layer so as to form a cathode layer; and 6) forming an anode layer on top of the electrolyte layer.
However, while the prior art focuses primarily on new suitable materials for use in solid oxide fuel cells, there still exists a need for an improved method of producing a solid oxide cell at a large scale, with which solid oxide cells can be produced very accurately at a high quality while minimizing waste material and waste product, thus being cost effective.